1. Field of the Invention
The present invention relates to a wear-resistant copper-based alloy, a cladding alloy, a cladding layer, and a valve system member and a sliding member for an internal combustion engine.
2. Description of Related Art
In order to avoid a problem of adhesion, a copper-based alloy is subjected to a certain surface treatment such as forming an oxide film on the surface of a metal. For example, under friction and wear conditions at a high temperature of higher than 200° C., there is a high probability of adhesive wear occurs due to contact between metals which are formed of materials with particularly low melting points. However, such a surface treatment is generally performed in a typical heat treatment process, and there is a problem in that time and production costs are needed.
Particularly in a case where a copper-based alloy is used as a cladding material of an exhaust valve seat for an ethanol-containing fuel such as gasoline, the copper-based alloy is placed in a reducing atmosphere in which a reduction action of hydrogen strongly works. Therefore, the formation of an oxide film formed of any one of molybdenum, tungsten, and vanadium, which contribute to wear resistance, niobium carbide, and the like is not promoted, and adhesive wear easily occurs due to contact between metals. When wear resistance decreases as described above, there may be a case where wear occurs to a degree beyond the limit that the valve seat functions.
In a case of adding chromium for the purpose of improving corrosion resistance, a chromium passive oxide film is formed on the surface of a copper-based alloy material and thus corrosion resistance is improved. However, an oxide film formed of niobium carbide and molybdenum and the like is less likely to be formed on the surface of the metal, and there is a problem in that wear resistance decreases.
For example, Japanese Patent Application Publication No. 8-225868 (JP 8-225868 A) discloses a wear-resistant copper-based alloy which contains 1.0% to 10.0% of chromium, and Japanese Patent No. 4114922 discloses a wear-resistant copper-based alloy containing 1.0% to 15.0% of chromium. In a wear-resistant copper alloy disclosed in Japanese Patent Application Publication No. 4-297536 (JP 4-297536 A), in a case of including chromium, it is considered that it is preferable to include chromium in a proportion of 1.0% to 10.0% in order to obtain the effect thereof. Similarly, in a wear-resistant copper alloy disclosed in Japanese Patent Application Publication No. 10-96037 (JP 10-96037 A), in a case of including chromium, it is considered that it is preferable to include chromium in a proportion of 1.0% to 10.0% in order to improve wear resistance.